The present invention is concerned with new and improved flat or planar batteries of the general type disclosed in U.S. Pat. Nos. 3,563,805; 3,617,387; 3,734,780; and the like.
As disclosed in the cited patents, in general such planar energy cells or batteries comprise superposed planar anode/cathode combinations possessing a separator disposed intermediate each anode and cathode and electrolyte disposed on or impregnated in the separator and in contact with respective facing surfaces of the anode and cathode.
Planar batteries of the type disclosed in the aforementioned U.S. patents are generally intended to be employed as an individual power source for portable electrically operated devices wherein the selected device design parameters are optimized by the availability and employment of a planar battery exhibiting reliability with respect to its power delivery characteristics. Batteries of the type in question presently are employed commercially to operate the various electrically powered systems of the photographic camera sold by Polaroid Corporation, Cambridge, Mass., U.S.A., under the trademark "SX-70". In such cameras, the battery, disposed as a component of a film pack for employment in and in combination with the camera, provides the electrical energy necessary to operate the camera's exposure control, film transport and photoflash systems and, accordingly, such battery is required to operate in a sequential series of power generating modes which may or may not be interrupted by more or less extended recovery and/or storage times and under which conditions to deliver the required series of high current pulses dictated by the photographic system design.
As disclosed in U.S. Pat. No. 3,543,662, and the like, such batteries may constitute a constituent component of a photographic film assembly which comprises a cassette configured to retain a predetermined number of film units for selective sequential photoexposure and a flat or planar battery for powering various photographic camera instrumentalities for photographic employment of the film units.
In present commercial employment, the planar batteries distributed comprise, in essence, primary batteries of the LeClanche type employing an aqueous electrolyte system which includes the conventional ionizable ammonium and/or zinc salt components of such type, e.g., ammonium and/or zinc chloride, and mercuric chloride present to inhibit the generation of hydrogen derived from electrolyte attack on LeClanche type zinc constituted battery anode materials.
Although the zinc anode battery materials are inevitably amalgamated with mercury to prevent electrolyte attack and that an ionizable mercury salt may be disposed in the electrolyte for amalgamation purposes, a certain percentage of the zinc anode material may be attacked by electrolyte with the concomitant release of hydrogen gas. In view of the critical necessity to maintain the various active layers and materials constituting a planar battery of the type set forth in the aforementioned U.S. patents, in intimate contiguous contact in order to reduce, to the extent possible, internal resistance within the cells constituting the battery, it is imperative that gas generated within the cells, which may distort the superposed relationship of the layers and materials, be effectively and expeditiously released from the battery in order to sustain its capacity and efficiency. In addition to hydrogen gas generation effecting separation between active layers and/or materials constituting the battery, the quantity of gas generated also may be such as to deleteriously effect the physical integrity of the battery, for example, by pressure rupture of the adhesive seals maintaining the physical conformation of the battery, with resultant environmental attack on, or loss of, active components constituting the battery's electrochemical system.